PHENOTYPIC STABILITY OF POTATO (SOLANUM-TUBEROSUM L) CULTIVARS GROWN UNDER DIFFERENT ENVIRONMENTAL-CONDITIONS IN THE SOUTHERN REGION OF THESTATE OF MINAS-GERAIS, BRAZIL

We evaluated the phenotypic stability of 14 potato cultivars (Achat, A gria, Apua, Baraka, Baronesa, Bintje, Bronka, Clarissa, Dunja, Frisia, Itarare, Monalisa, Radosa, and Ruta) for marketable tuber yield and i ts components (number of marketable tubers per plot and mean tuber wei ght). The contribution of environmental effects to the genotype x envi ronment interaction was also evaluated. Trials were carried out in nin e environments (locations, years and planting dates) in a fully random ized block design with four replications. The cultivars Bronka, Monali sa and Clarissa were the most stable for marketable yield. Cultivars B araka, Bronka and Monalisa were the most stable for mean marketable tu ber weight. Bintje and Achat, which are among the three cultivars most frequently planted in the region, proved to be highly unstable both f or yield and for mean tuber weight. For number of marketable tubers pe r plot, the regression model was not satisfactory to evaluate the phen otypic stability of cultivars due to the low values for the determinat ion coefficients (average r2 = 0.47). Among the environmental effects that contributed to the genotype, x environment interaction, planting date was more important than location and the effect of location was g reater than years. Mean marketable tuber weight was the trait least af fected by genotype x environment interaction.